This project will investigate the development transitions of the internalized structures of representation in children's concepts of their naturalistic experience. The research will use both an ethological and an experimental approach to children's nonlogical and "primitive" conceptual systems, and will give programmatic attention to the affective and social ingredients of their cognitive capacities. Older subjects will also be used to explore the persistence of naturalistic thinking beyond childhood. Both verbal and nonverbal methods will be used to assess the subjects' conceptions of three distinct qualitative categories or areas of experience: unlimited properties of existence, restricted hierarchies, and unitary categories. A verbal dialogue with many different types of questions, corresponding to different components of conceptual meaning, will in some cases be supplemented with propositional techniques such as role-playing or sentence-construction. Finer details of the structure of concepts will be obtained with more highly controlled nonverbal tasks of sorting, grouping by exclusion, and forced choice discrimination (all using very high-fidelity three-dimensional miniaturized replicas of common objects). Some of the nonverbal tasks may also be converted to experimental acquisition paradigms for modification of children's conceptual capacities.